Formation and scission of the sulfur–sulfur bond: a new approach to reactions between sulfur/polysulfide ions and thiolate ions/disulfides in N,N-dimethylacetamide

Abstract

The reactivity of sulfur towards a series of thiolate ions RS^–[R = phenyl (1), 4-methylphenyl (2), benzyl (3) ethyl (4), propyl (5), butyl (6), sec-butyl (7), tert-butyl (8)] has been studied by spectroelectrochemistry in N,N-dimethylacetamide. Apparently, sulfur reacts in two parallel ways: (i) oxidation of RS^– leading to RS₂R and S₃˙^– ions; (ii) preponderant S-nucleophilic process yielding stable RS_x^– ions (x= 2–5). RS_x^– species, whose spectrophotometric characteristics have been determined, are successively obtained in the course of sulfur addition with R = alkyl, whereas equilibria between arylpolysulfide ions were observed. At the junction of these two parallel pathways, the slow key equilibrium 2RS₄^–⇌ RS₂R + 2S₃˙^– has been investigated by addition of RS₂R R = 1–8 to S₃˙^– solutions. In fact, our study is consistent with at first, a monoelectronic transfer between RS^–(or RS₂^–) ions and the very reactive S₂ molecules in equilibrium with S₈. The fast and competing couplings of the radicals RS˙(or RS₂˙), S₂˙^–(or S₃˙^–) agree with the simultaneous formation of RS₂R, RS_x^– and polysulfide ions. More generally, the S₂/S₂˙^– redox system is believed to be involved in thiophilic reactions of a number of anions such as RS^– towards sulfur rather than the initial opening of the cyclic S₈ form.